Paeonol improves renal and vascular angiotensin II type 1 receptor function via inhibiting oxidative stress in spontaneously hypertensive rats

Background Oxidative stress has been shown to play a critical role in the pathogenesis of hypertension. Paeonol, a major phenolic component extracted from Moutan Cortex, exerts a beneficial effect in preventing cardiovascular disease via reducing oxidative stress. The present study investigated the protective mechanism of paeonol against high blood pressure in spontaneous hypertension rats (SHRs). Methods Wistar-Kyoto (WKY) rats and SHRs received vehicle or peaonol in the drinking water for 5 weeks. Blood pressure was measured by tail-cuff plethysmography and oxidative stress in kidney and vascular tissue was examined by enzyme-linked immunosorbed assay. The functions of angiotensin II type 1 receptors (AT(1)R) in the kidney and mesenteric artery were measured by natriuresis and vasoconstrictor response, respectively. Results Compared with vehicle-treated WKY rats, vehicle-treated SHRs exhibited higher blood pressure, increased oxidative stress, accompanied by exaggerated diuretic and natriuretic responses to candesartan (AT(1) receptor antagonist) and vasoconstrictor responses to angiotensin II (Ang II). Moreover, SHRs had higher ACE and AT(1)R in the kidney and mesenteric artery, and higher Ang II and lower renin levels. Interestingly, paeonol treatment reduced the candesartan-induced increase in diuresis and natriuresis and vasoconstrictor responses to Ang II, and lowered blood pressure in SHRs, accompanied by reducing AT(1)R protein expression in the kidney and mesenteric artery of SHR, and Ang II levels in plasma and increasing renin levels in renal cortex. In addition, these changes were associated with reducing oxidative stress. Conclusions The present study suggests that paeonol improves renal and vascular AT(1)R functions by inhibition of oxidative stress, thus lowering blood pressure in SHRs.